Sending, receiving, and organizing email in Outlook.com
@Craig Litz said
When sending email to myself ... showing that it came from my default outlook.com address rather than my primary email address
If this is about different accounts, then the answer from TaoLi is accurate.
If this is about multiple aliases for a single account, the you need to change your default "Send From" alias. You do it using Outlook Web, but the change will take effect on all of your Outlook clients.
If you see a [Sign in] button - do it.
Email aliases -> Set default From address
- Select your the alias you want to use as your default "From".